1. Field of the Invention
The present invention relates to an air-intake device for an internal combustion engine, as represented by an engine for an automobile or the like. In particular, the present invention relates to a countermeasure for making it possible, with an internal combustion engine equipped with a plurality of groups of cylinders such as a V-type internal combustion engine or the like, to manifest the beneficial effects of resonant supercharging, while still adequately maintaining the air/fuel ratio of the mixture gas in each cylinder.
2. Description of the Related Art
An internal combustion engine (an engine) like the ones disclosed in, for example, Japanese Patent Application Publications Nos. JP-A-5-332143 or JP-A-11-117750, equipped with an air-intake system which takes advantage of the beneficial effects of resonant supercharging, is per se known. In detail, surge tanks which are provided to each of the banks of, for example, a V-type engine are communicated together by a communication conduit (a resonance conduit). In the interior of this communication conduit, there is provided an opening and closing valve (a resonance valve). And this opening and closing valve is opened in the engine speed region in which the beneficial effects of resonant supercharging are considered to be required, so that, by the surge tanks communicating with one another via the communication conduit, it is arranged for the effects of resonant supercharging to be manifested. By doing this, with an engine which takes advantage of the beneficial effects of inertial supercharging, it becomes possible by the effects of resonant supercharging, for example, to eliminate downturn of the torque in a specified engine speed region in which these effects of inertial supercharging cannot be sufficiently obtained.
Furthermore, the above described V-type engine is known as one engine configuration. As one type of air-intake system for such a V-type engine, there is known one which comprises a independent air-intake system for each bank (a dedicated air-intake system for each bank). In other words it comprises, for each bank independently, an air-intake system which comprises, in order from the upstream side of the intake passage, an air cleaner, an air flow meter, a throttle valve, a surge tank, and an intake manifold; i.e., two air-intake systems. If an independent air-intake system is provided for each bank in this manner, it is possible to obtain a comparatively large air cleaner volume with respect to the amount of air which is to be inducted into each of the banks, and accordingly it is possible to reduce the pressure loss in the air-intake system. Due to this, there is the beneficial effect that it is possible sufficiently to ensure the amounts of air charged into the cylinders. Furthermore, it is possible to detect the amount of intake air into each of the banks separately and moreover accurately with its own corresponding air flow meter. Because of this, there is also the beneficial effect that it becomes possible to bring the actual air/fuel ratio (A/F) for each of the banks close to the target A/F at high accuracy. It should be understood that, with an engine which is equipped with this type of air-intake system, an ECU is provided to each bank in order to control the fuel injection amounts to the injectors and the ignition timings of the spark plugs, and it is arranged to be able to ensure the controllability of the above described fuel injection amounts and ignition timings in a satisfactory manner.
Now, when an air-intake system which takes advantage of the above described resonant supercharging effect is applied to a V-type engine which is equipped with the above described type of air-intake system having two independent systems, malfunctioning such as described below can occur.
That is to say, with an air-intake system which takes advantage of the resonant supercharging effect, the opening and closing valve is opened in the engine speed region in which this resonant supercharging effect is required, and the surge tanks are communicated together by the communication conduit. In other words, flow of air from each one of the banks to the other becomes possible via the communication conduit. In this case, in a situation in which the internal pressures inside the surge tanks are mutually different, air comes to flow from that surge tank whose internal pressure is high towards that surge tank whose internal pressure is low. In other words, on the one hand, the amount of intake air to the cylinders which are connected to that surge tank whose internal pressure is high is decreased by the amount of this air inflow described above, while, on the other hand, the amount of intake air to the cylinders which are connected to that surge tank whose internal pressure is low is increased by the amount of this air inflow described above. Since this phenomenon is created on the downstream side of the above described air flow meters, a deviation occurs in the amounts of intake air which are actually sucked into the cylinders of each bank with respect to the amounts of intake air which are detected by the air flow meters provided to each of the banks, which is undesirable. Moreover, for each cylinder of each bank, its fuel injection amount is determined according to its intake amount as detected by the air flow meter at its respective upstream side. Due to this, for those cylinders for which the amount of intake air has decreased by just the amount of the above described air inflow, the A/F comes to deviate to the rich side with respect to the target A/F. On the other hand, for those cylinders for which the amount of intake air has increased by just the amount of the above described air inflow, the A/F comes to deviate to the lean side with respect to the target A/F.
As a result, a satisfactory state of combustion of the mixture gas inside the cylinders cannot be obtained. Not only does this decrease the engine output, but there is also something of inviting malfunctioning, in which it becomes impossible to maintain the temperature of a catalytic converter which is provided in the exhaust system at an adequate temperature so that it becomes impossible to obtain a sufficient performance therefrom, or in which the spark plugs get into a state of being wetted with fuel in the liquid phase (the so called flooded state of the spark plugs) so that the state of ignition of the mixture gas deteriorates, or the like.